The invention relates to an inductive rotary emitter for the control, especially of the ignition timing, of internal combustion engines, having a coil with a permanent-magnetic core and a yoke wheel rotated by a shaft and bearing tooth-like segments projecting from and distributed about its circumference and moving past the magnetic poles for the induction of voltage. The invention furthermore relates to a method for the ignition of internal combustion engines, especially in lawn mowers, power saws and cut-off grinders, in which such a rotary emitter is used. The invention lastly relates to a condenser ignition system having a rotary emitter of said kind.
In known condenser ignition systems the operation of the electronic switch is produced either by an external igition pulse emitter or by an internal ignition pulse emitter which, for example, produces the necessary ignition signal from the charge in the condenser through a voltage divider. It is common to control the ignition timing according to the operating state of the internal combustion engine, especially according to its rotatory speed. The use of the above-mentioned segment wheels coupled to the crankshaft of a gasoline engine is known for this purpose; these wheels are yoke wheels formed from high-permeability, ferromagnetic material from whose circumference uniformly distributed tooth-like segments project radially or axially. The segments cooperate with the pole shoes of a permanent magnet which is surrounded by a coil. As soon as the yoke wheel rotates, an alternating current is induced in the coil on account of the variation of the air gap between the pole shoes and the yoke wheel and hence of the magnetic flux passing through the coils. To trigger a spark, an additional magnetic rod or the like must be provided in the case of the known yoke wheels in order to inform the unit that fires the spark of the angular postion of the yoke wheel.